It sounds like something out of a science-fiction movie, but the Chicago Police Department says its crime-predicting computer algorithm helped them carry out the largest gang raid in recent memory.

Police Superintendent Eddie Johnson announced on May 20 that police had arrested 140 people on drug and weapons charges with the help of the Strategic Subject List (SSL).

That list is compiled by a computer that examines a person's history and life then gives them a 'danger rating' - and it has left a civil liberties group horrified, Yahoo News reported Wednesday.

Predictions: With violent crime rising in Chicago, police have taken to using predictive software to avoid scenes like these. Their algorithm looks at a person's history and associates and gives them a danger rating

'There’s a police database that’s populated with secret information, and people can’t challenge the accuracy of it. That’s where our concern is,' Karen Sheley, director of the Police Practices Project for the American Civil Liberties Union of Illinois, told Yahoo News.

'What we have now is a list based on information that isn’t made public, and we know that people can’t protest being on it in any way.'

Built by the Illinois Institute of Technology, the software looks at an individual's criminal record, gang affiliations and network, then puts them on the SSL with a rating out of 500 - the higher the number, the more dangerous they are.

It does not take into account their race, age, sex or neighborhood, police said.

The technology has been likened to to Tom Cruise film 'Minority Report,' in which police use psychics to arrest potential murders before they can commit their crime.

Of course, that's not an option for the real-life cops, who instead use it to identify people they need to keep an eye on.

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That's what led to the raid earlier this month, in which police brought in 23 weapons, $45,000 in drugs and 140 people - 95 of whom were documented gang members and 117 of whom were on the SSL.

And police say that beyond that bust, more than 70 percent of those arrested for murder, more than 80 percent of those arrested for shooting crimes and more than 74 percent of shooting victims were on the SSL.

The startling use of technology is necessary, some believe, due to the ever-rising levels of violence in the city, which saw 51 homicides in January - the largest since 2000 - and a total of 468 murders last year, an increase of 12.5 percent on the year before.

Police also say that they put the algorithm to work proactively, trying to dissuade at-risk people from committing crimes, either with home visits or by calling in people on parole or in gangs.

'We try to educate this population on the lifestyle that they’re in and warn them. We’re giving them a chance to turns their lives around.' Anthony Guglielmi, director of communications for the Chicago Police Department, said.

Concerns: A spokesperson for the American Civil Liberties Union of Illinois said she was concerned by the secret database, which is not open to the public and which people cannot examine or refute